The challenge to commercial broadcasters posed by satellite radio and the iPod has increased significantly as Pandora Radio and its rivals stream music over growing numbers of smartphones, tablets and laptops.

"Pandora is more than two-thirds of all Internet radio all by itself," said Larry Rosin, president of Edison Research, a media research provider.

He added that Pandora "is clearly stealing time from commercial radio music stations, primarily among people under 35 years old."

For San Antonio-based CC Media Holdings, the threats from new technology are compounded by a $20 billion debt load carried over from when it was taken private in a leveraged buyout.

The broadcasting and outdoor advertising giant, which owns more than 800 radio stations, said recently it posted a $191 million loss in the fourth quarter of 2012.

"The biggest problem facing the corporate owners of radio stations is that they are smothered by debt," said Michael Harrison, publisher of RadioInfo trade publication.

But Harrison said the iPod and other devices have had a big role in cutting into radio's influence over what music is discovered and becomes ingrained in culture.

"Radio used to be the place that people went to as their primary source to hear music ... and to find out what's going on in music," he said.

While the percentage of the population listening to radio has stayed nearly constant over the last decade, time spent listening to the radio has declined by about 15 minutes a year for the last 20 years, said Larry Johnson, senior research consultant for Paragon Media Strategies.

The drop has been pronounced among younger listeners, but Johnson said there's no clear way to see if those declines have been caused by listeners leaving radio for online streaming services.

"You have more choices and, of course, the time spent listening is going to go down," he said. "But when you step back, radio is still very strong, though not as big of a deal as it was in 1989."

A study by the Katz Radio Group provided by Johnson showed listeners age 18 to 34 listened to 15.25 hours of broadcast radio every week during spring 2011, while listeners between 35 and 64 listened to 17.5 hours.

The three largest U.S. radio companies - Clear Channel Communications, an arm of CC Media Holdings; Cumulus Media; and CBS Radio - are trying to get a foothold in online streaming.

Clear Channel has put the marketing muscle of its 800 radio stations behind its iHeartRadio apps, which allow users to create their own music stations, like Pandora, and provides live feeds from all its stations.